1. Field of the Invention
The present invention relates to a smoke detecting apparatus for detecting occurrence of smoke by subjecting an image captured by a monitoring camera to image processing, and more particularly, to a smoke detecting apparatus capable of avoiding false detection and detection failure due to an effect of disturbance.
2. Description of the Related Art
Early detection of fire or smoke is very important in view of early fire control upon occurrence of a fire, and in view of preventing trapping in a fire accident. Therefore, in the field of smoke detecting apparatuses, studies have been conducted for early smoke detection by subjecting an image captured by a monitoring camera to image processing.
As an example, there has been known a smoke detecting apparatus for detecting smoke by installing a camera in a tunnel or the like and subjecting an image captured by the camera to image processing. In the image processing for detecting smoke, generally, an image to be used as reference (reference image) is previously stored, a differential image between a most recently captured image and the reference image is calculated, and a region in which a change has occurred is extracted, to thereby detect smoke (see, for example, JP 3909665 B).
Further, in order to adapt to a temporal change of the reference image due to an effect of sunshine or the like, the reference image is periodically updated.
By detecting smoke by subjecting an image captured by a camera to image processing, the following two advantages may be obtained.
1) By visually checking the image of the monitoring camera, smoke detection status may be grasped at a remote site.
2) It is possible to use a monitoring camera that is already installed, resulting in an efficient use of facility.
However, the related art has the following problems.
Conventionally, in order to detect smoke, a pixel region having a luminance difference from a frame differential image or background image above a predetermined threshold has been extracted. However, there has been a problem in that, for example, when the captured image changes due to an effect of a change in surrounding illumination condition or the like, a portion with no occurrence of smoke may be falsely detected as smoke.
In addition, the smoke itself as a detection target is pale and may have a small luminance change (luminance difference) in the captured image depending on the background color. Therefore, simply determining the differential image alone may not allow smoke detection at high sensitivity because the threshold setting for the luminance difference is difficult.
Further, the image is preferably captured by the monitoring camera in an environment where the illumination condition and a field of view are always stable. However, the location to be monitored may not always have such good conditions. Moving objects such as people may come and go in a monitoring range in one location, or the sunshine condition may change with time in another location, to thereby render a partial area of the monitoring range unsuitable for monitoring.
According to the related art, the smoke detection is performed with the same judgment criterion even for the area unsuitable for monitoring, and the effect due to intrusion of the moving object or the change in sunshine condition (effect of disturbance) may be falsely detected as the smoke occurrence. It is also possible to divide the image into a matrix of regions of a predetermined size and mask the area (region) unsuitable for monitoring to be excluded from the smoke detection, but the masking results in limiting the range that may be monitored.